Your best bet is to get into the doctor or urgent care clinic today to have the sore swabbed. If this developed over the last few days, it could still over a viable sample for hsv swabbing.
When you were tested 3 weeks ago, was hsv testing included? Most standard std panels do not include hsv unless specifically requested. You might want to confirm that and confirm if it was an IgG test.
9 hours is really quick for symptoms to show up but if you haven’t had sex in the weeks prior to that, then it wouldn’t be typical for hsv. Not impossible I suppose but rare.